Wood is a fibrous tissue, found in the stems of woody plants such as trees and shrubs. According to an article by the University of Minnesota Extension, wood is generally composed of cellulose (about 50%), hemicellulose (about 15%-25%), and lignin (about 15%-30%). (http://www.extension.umn.edu/distribution/naturalresources/components/6413chl.html.)
Wood is used in a very wide variety of applications, for example as construction materials (including framing lumber, decorative woodwork, flooring, and the like), in boats, toothpicks, gunstocks, cabinets, furniture, sports equipment, and parts for weaving and knitting mills. Moreover, many products are made by processing wood or wood fiber into other materials. For example, many products are made by dispersing wood fiber in a resin matrix, including composite construction materials such as beams, particleboard, composite flooring materials, and many other products that are used as substitutes for wood. Other products are made from wood layers adhered together, for example plywood and glued wood laminates such as veneers.
Wood has a number of advantages compared to other materials such as metal, plastic and concrete. For example, trees are a renewable resource, the cultivation of which offsets carbon emissions and preserves wildlife habitat. Moreover, wood has aesthetic qualities that are desirable for many applications, such as flooring and furniture, and exhibits a good strength-to-weight ratio and good resiliency (as compared, for example to metal or concrete). Wood also generally exhibits good thermal, sound, and electrical insulating properties.
Different types of wood exhibit different mechanical and aesthetic properties, and have different costs. For example, different types of woods exhibit widely different strengths, hardness and flexural properties. Softer woods that have a lower flexural modulus generally are available at lower cost, and may in some cases have desirable aesthetic properties, but are unsuitable for some applications due to their mechanical properties.